Sub species: leniusculus (Signal crayfish): Astacus leniusculus was placed on the Official List of Specific Names in Zoology, name number 2244, in Opinion 855 of the International Commission on Zoological Nomenclature. (See Melville, 1968: 84). klamathensis (Klamath Signal Crayfish) trowbridgii: (Columbia River Signal Crayfish)

Recent genetic studies (Crandall lab) suggest that these different subspecies are in fact distinct. Thus the P. klamathensis and P. trowbridgii might themselves be endangered whereas the P. leniusculus is more broad spread and indeed an invasive.

Justification:Pacifastacus leniusculus has been assessed as Least Concern. This is an invasive, r-selected and widespread species, which is able to out-compete native species often growing to a larger size. This species is also resistant to the crayfish plague but is a carrier of the disease and is able to thrive in a wide range of habitats. It has been introduced into Europe and outside of its native range in the USA. No conservation measures are required.

Pacifastacus leniusculus leniusculus is distributed throughout British Columbia in Canada, and in California, Idaho, Oregon, and Washington in the USA. Pacifastacus leniusculus klamathensis is distributed throughout British Columbia in Canada, Idaho and south to central California in the USA. Pacifastacus leniusculus trowbridgii is distributed throughout British Columbia in Canada and California, Idaho, Oregon and Washington in the USA, and has been introduced into California and Nevada in the USA, and also introduced into Japan. Furthermore, this species is also known to occur in Greece (Koutrakis et al. 2007).

Pacifastacus leniculus has been introduced into many countries throughout Europe, as well as to California, Nevada and Utah in the USA. This species was introduced during the 1970s and 1980s, is widely cultivated and is established in the wild, from where it is harvested (Harlioğlu and Holdich 2001).

There is no population information for Pacifastacus leniusculus; however the signal crayfish is an important invasive species, which has a wide distribution and is likely to exceed 1 million mature individuals in the wild.

Pacifastacus leniusculus leniusculus generally prefers cool water with current over a rocky bottom; does not burrow; is highly adaptable and can be found in a wide variety of habitats including coastal and mountain streams and lakes, reservoirs, and the saline waters in river deltas (Hogger 1988). Pacifastacus leniusculus klamathensis is found in lentic and lotic habitats including cold swift streams. Pacifastacus leniusculus trowbridgii is found in lentic and lotic habitats.

Tolerance experiments indicated that O+ juveniles and adults are well adapted for surviving salinities of at least 21 in the long term and of being transferred directly back into freshwater. However, their ability to colonize the estuarine environment may be restricted to areas of low salinity (i.e. 7) due to the adverse effects of seawater on egg development and hatching (Holdich et al. 1997).

There are no species-specific conservation measures in place for Pacifastacus leniusculus; however, in places its distribution coincides with protected areas. This species is highly adaptable, widespread throughout the world, invasive and is a vector of the crayfish plague. This species is generally regarded as a threat to native species and does not require any conservation measures.